Container for molten metal, use of the container and method for determining an interface

ABSTRACT

A container for molten metal is provided with a temperature measuring device arranged in an opening of a container wall. The temperature measuring device has a protective sheath, which projects into the container and which is closed at its end arranged in the container. A temperature measuring element is arranged in an opening of the protective sheath. The protective sheath is composed of a mixture of a heat-resistant metal oxide and graphite, and the closed end is spaced at least 50 mm from the container wall.

BACKGROUND OF THE INVENTION

The invention relates to a container for molten metals with atemperature measuring device arranged in an opening of a container wall,wherein the temperature measuring device has a protective sheath, whichprojects into the container and which is closed at its end arranged inthe container, and a temperature measuring element arranged in anopening of the protective sheath. In addition, the invention relates tothe use of the container, as well as to a method for determining aninterface between two materials arranged one above the other in acontainer, particularly between a slag layer and underlying steel melts.

Such containers are known from the prior art. For example, it is knownfrom German Utility Model GM 72 28 088 to arrange a thermocouple in awall of a steel ladle. The thermocouple is arranged in a steel tube,which is surrounded by a ceramic protective layer. German Patent DE 1054 735 discloses a smelting crucible for metals, in whose side wall atemperature sensor is inserted. The temperature sensor has a protectivetube made of a metal-ceramic material, such as molybdenum and aluminumoxide. The protective tube projects with its tip approximately 25 mminto the side of the smelting space. U.S. Pat. No. 3,610,045 discloses asmelting crucible for molten iron, in whose side wall a thermocouple isarranged. The thermocouple is protected by a conical protective sheathmade of aluminum oxide and silicon oxide. A similar container is knownfrom European Patent EP 314 807 B1. Also in this container, athermocouple is led through the wall into the interior of the container.The thermocouple is protected by an aluminum oxide tube which, in turn,is surrounded by a boron nitride protective sheath in the interior ofthe container.

From U.S. Pat. No. 6,309,442 B1 a container for molten metals is known,on whose inner side contacts made of zirconium dioxide or thoriumdioxide are arranged one above the other, in order to measure the levelof the interface between the molten metal and the slag.

BRIEF SUMMARY OF THE INVENTION

The invention is based on the problem of improving a container formolten metals, such that the temperature of the melt located therein canbe measured as accurately as possible over a longer time period. Theinvention is further based on the problem of further improving the knownmethod for determining the interface level.

According to the invention, the problem is solved by a container formolten metal with a temperature measuring device arranged in an openingof a container wall, wherein the temperature measuring device has aprotective sheath, which projects into the container and which is closedon its end arranged in the container, and a temperature measuringelement arranged in an opening of the protective sheath, characterizedin that the protective sheath comprises a mixture of a heat-resistantmetal oxide and graphite and that the closed end is spaced at least 50mm from the container wall.

Therefore, because the container characterized above has a protectivesheath made of a heat-resistant metal oxide and graphite, and becausethe closed end of the protective sheath is spaced at least 50 mm,preferably approximately 75 to 200 mm, from the container wall, theactual temperature of the molten metal can be measured without coolingeffects, possibly coming from the crucible wall, influencing themeasurement values. At the same time, the protective sheath issufficiently resistant to aggressive molten metal, particularly moltensteel, and thus is suitable for long-term use.

The temperature measuring element with the protective sheath canpreferably be arranged in the base (floor) of the container, so that itcan also be used for measurements with low filling levels. Theprotective sheath preferably consists essentially of aluminum oxide andgraphite, wherein aluminum oxide can comprise particularly a portion ofapproximately 20 to approximately 80 wt. % and graphite a portion ofapproximately 5 to approximately 60 wt. %. The protective sheath canalso contain carbon in a different form than graphite and/or otherrefractory oxides.

Within the protective sheath, it is beneficial if the temperaturemeasuring element, preferably a thermocouple, is surrounded by aprotective tube, which is preferably formed of aluminum oxide. It isbeneficial if the outer diameter of the protective tube is approximately0.1 to 1 mm smaller than the inner diameter of the opening of theprotective sheath. The protective sheath can have, at least in one partof its length, an outer conical form with a diameter becoming smallertowards the interior of the container, in order to enable securemounting in the container wall and sufficient stability of theprotective sheath.

Furthermore, it can be beneficial if a sensor projecting into theinterior of the container is arranged on the protective sheath fordetermining a change in material or a change of material properties,particularly an electrochemical, electromagnetic, or optical sensor or asensor for detecting an electrical voltage and/or an electrical currentand/or an electrical resistance. In this manner, interface measurementsbecome possible between the molten metal, particularly the molten steel,and the above-lying slag.

As soon as the sensor touches the interface, the signal picked up by thesensor changes and thus indicates that the interface has been reached.Furthermore, it can be advantageous if a bushing made of refractorymaterial, preferably made of mullite, is arranged in the opening of thecontainer wall between the container wall and the protective sheath,wherein the bushing can have a conical shape with a diameter becomingsmaller towards the interior of the container.

According to the invention, the container can be used as a foundryladle, particularly for molten steel. The molten metal is always movingin a foundry ladle, a so-called tundish, so that a particularly highstability is required for the measuring device projecting relatively farinto the container. The foundry ladle is typically pre-heated, so thatthe measuring device is also pre-heated. This leads to very shortreaction times, so that the temperature measuring device very quicklyreaches its equilibrium temperature with the melt, and the measurementcan be performed very quickly.

The problem is solved for the method characterized at the outset in thata sensor for determining a change in material or a change of materialproperties, particularly an electrochemical, electromagnetic, or opticalsensor or a sensor for detecting an electrical voltage and/or anelectrical current and/or an electrical resistance is arranged withinthe lower material contained in the container. The measurement signal ofthe electrochemical sensor is measured during the pouring out or outflowof the material from the container, and a change in the signal isestablished when the sensor contacts the interface between thematerials. Preferably, the signal change is associated with the distanceof the interface from the floor of the container. In addition, it can bebeneficial if the pouring or outflow process is ended when the signalchanges. For this purpose, the measurement signal is simultaneously usedto send a signal to the device controlling the pouring or outflowprocess, on the basis of which the pouring or outflow process isterminated.

Despite the relatively large length by which the protective sheathprojects into the melt, the device has sufficient stability, so that ameasurement of the temperature of the molten metal and a measurement ofthe position of the interface between the molten metal and theabove-lying slag is possible.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown. In thedrawings:

FIG. 1 is a view of a longitudinal cross section through the temperaturemeasuring device, according to an embodiment of the invention, arrangedin the container wall; and

FIG. 2 is a partial longitudinal view of the closed end of thetemperature measuring device with electrochemical sensor, according toan embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The measuring device according to one embodiment of the invention has abushing 1 made of mullite. This is arranged in the floor of a foundryladle for molten steel, which is not shown for reasons of clarity. Suchfoundry ladles are known in expert circles, for example from the alreadymentioned U.S. Pat. No. 6,309,442 B1 (cf. FIG. 1, numeral 16). Theprotective sheath 2 is arranged in the bushing 1. The protective sheath2 consists essentially of a mixture of aluminum oxide and graphite. Theprotective sheath 2 has a conical profile at least in the part arrangedin the bushing 1. This enables easier removal from the bushing 1 forexchanging the protective sheath 2 with the temperature measuringelement 3. The temperature measuring element 3 is surrounded by a closedaluminum oxide tube 4 within the protective sheath 2.

The protective sheath 2 is fixed into the bushing 1 by refractory cement5. The tip of the protective sheath 2 projects approximately 120 mm intothe foundry ladle, so that the measurement performed at the tip of thetemperature measuring element 3 remains uninfluenced by wall effects ofthe foundry ladle. The end of the temperature measuring element 3 facingaway from the interior of the foundry ladle has a so-called connector 6,which serves as the mechanical and electrical contact with the measuringelement 3. The entire arrangement made of the mullite of the bushing 1and the protective sheath 2 fixed by the cement 5 comprises a dense,powder-free material, so that there is no leakage in case a break of onepart of the arrangement occurs, and molten metal cannot escape from thefoundry ladle.

FIG. 2 shows the tip of the protective sheath 2, which projects into thefoundry ladle, with the temperature measuring element 3 and anelectrochemical sensor 7. The electrochemical sensor 7 projects out ofthe protective sheath 2 and is fixed with refractory cement 8. Thealuminum oxide tube 4 is also fixed in the refractory cement 8. Theelectrochemical sensor is a typical electrochemical sensor having azirconium dioxide tube 9 as solid electrolyte material, in which thereference electrode 10 is arranged in a reference material 11 and afilling material 12. Such electrochemical sensors are known inprinciple, for example from U.S. Pat. No. 4,342,633.

The temperature measuring element 3 is formed from a thermocouple,wherein the outer sheath comprises aluminum oxide, and one of the twothermal wires 13 extends into an aluminum oxide tube 14 that is open onboth sides. All of the electrical lines lead through the aluminum oxidetube 4 into the connector 6 and can be further connected there to ameasuring device.

The voltage generated by the electrochemical sensor 7 essentiallydepends on the measurement environment. Therefore, a change in voltageoccurs immediately as soon as this environment changes. This is thecase, for example, when the liquid level of the molten steel located inthe foundry ladle falls and the electrochemical sensor 7 comes intocontact with the slag layer arranged above the melt. Therefore, an exactdetermination of the height of this interface between the molten steeland slag above the floor of the foundry ladle is possible. As soon asthe electrochemical sensor 7 detects the interface, for example byanother signal, the outflow of the molten steel from the foundry ladlecan be terminated by closing the outlet.

Fundamentally, it is also possible to arrange several electrochemicalsensors 7 over the periphery of the protective sheath 2 spaced in thelongitudinal direction, so that the change of the bath level of themolten metal can also be established. Instead of an electrochemicalsensor, other sensors can also be used for establishing the change ofthe material properties in the interface region of the molten steel andslag, particularly electrochemical, electromagnetic, or optical sensorsor sensors for detecting an electrical voltage and/or an electricalcurrent and/or an electrical resistance.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A container for molten metal comprising a temperature measuringdevice arranged in an opening of the container wall, wherein thetemperature measuring device has a protective sheath, which projectsinto the container and which is closed on its end arranged in thecontainer, and a temperature measuring element arranged in an opening ofthe protective sheath, wherein the protective sheath comprises a mixtureof a heat-resistant metal oxide and graphite, and wherein the closed endis spaced at least 50 mm from the container wall.
 2. The containeraccording to claim 1, wherein the closed end is spaced approximately 75to 200 mm from the container wall.
 3. The container according to claim1, wherein the temperature measuring device is arranged in a part of thecontainer wall forming a floor of the container.
 4. The containeraccording to claim 1, wherein the protective sheath consists essentiallyof aluminum oxide.
 5. The container according to claim 1, wherein theprotective sheath consists essentially of aluminum oxide with a portionof approximately 20 to approximately 80 wt. % and graphite with aportion of approximately 5 to approximately 60 wt. %.
 6. The containeraccording to claim 1, wherein a protective tube is arranged in theprotective sheath.
 7. The container according to claim 6, wherein theprotective tube comprises aluminum oxide and surrounds the temperaturemeasuring element,
 8. The container according to claim 1, wherein theprotective sheath has at least on one part of its length an outerconical form with a diameter becoming smaller toward an interior of thecontainer.
 9. The container according to claim 1, wherein thetemperature measuring element is a thermocouple.
 10. The containeraccording to claim 1, further comprising a sensor projecting into theinterior of the container for determining a change in material, whereinthe sensor is arranged on the protective sheath.
 11. The containeraccording to claim 10, wherein the sensor is at least one selected fromthe group consisting of an electrochemical sensor, an electromagneticsensor, an optical sensor, and a sensor for detecting at least one of anelectrical voltage, an electrical current and an electrical resistance.12. The container according to claim 1, further comprising a bushingmade of refractory material and having a conical shape with a diameterbecoming smaller toward an interior of the container, wherein thebushing is arranged in the opening of the container wall between thecontainer wall and the protective sheath.
 13. The container according toclaim 12, wherein the bushing comprises mullite
 14. The containeraccording to claim 1, wherein the container is a foundry ladle formolten steel.
 15. A method for determining an interface between twomaterials arranged one above another in a container, the methodcomprising arranging within the lower material a sensor for determininga change in material, and measuring a measurement signal of the sensorduring pouring or outflow of the material from the container, such thata change in signal is established when the sensor contacts the interfacebetween the materials.
 16. The method according to claim 15, wherein theinterface is between a slag layer and an underlying molten steel. 17.The method according to claim 15, wherein the sensor is at least oneselected from the group consisting of an electrochemical sensor, anelectromagnetic sensor, an optical sensor, and a sensor for detecting atleast one of an electrical voltage, an electrical current and anelectrical resistance.
 18. The method according to claim 15, wherein thechange in signal is associated with a distance of the interface from afloor of the container.
 19. The method according to claim 15, whereinthe pouring or outflow of the material is terminated when the signalchanges.